This invention relates to the preparation of 2-substituted-1,3-dioxacycloalkanes, also known as "acetonides". In particular, this invention relates to such a process wherein the reactants are a diol and a diunsaturated ether.
2-Substituted-1,3-dioxacycloalkanes, hereinafter referred to as DOCA's, are useful in a number of respects.
In the synthesis of many organic compounds, a diol compound must undergo certain reactions without "damaging" the alcohol moieties. If these reactions would cause damage to the alcohol moieties, a typical approach is to first "block" or "protect" the hydroxyls by reacting them with a group which is inert in the reaction that can damage bare hydroxyls, but which can be easily removed, yielding the hydroxyl functionality, at a later time. When the compound to be protected has at least 2 hydroxyl moieties, the formation of a DOCA is an excellent method of protecting the compound.
Further, in the manufacture of certain compounds, such as pesticides, a DOCA moiety is an important part of the final compound.
DOCA compounds and their syntheses are not unknown. Typical synthesis routes employ a diol and a second reagent, and may also require a catalyst, heat, pressure, or other reaction conditions.
Larson and Hernandez, J. Org. Chem., Vol. 38, No. 22, p. 3935 (1973), disclose a method where unsaturated trimethylsiloxy compounds are reacted with diols to yield DOCA's in a mildly exothermic reaction. This reference claims yields of 70 to 80 percent. The principal by-product is trimethylsilanol.
Ball, Biochemical Preparation, published by John Wiley & Sons, pp. 31-34 (1952), is representative of many references which teach the formation of DOCA's with alkanones (ketones) such as propanone (acetone), in the presence of a catalyst such as ZnCl.sub.2.
Debost, Gelas, and Horton, J. Org. Chem., Vol. 48, p. 1381 (1983), teach the formation of DOCA's with 2-alkoxypropenes. This has a small positive free energy, but its main disadvantage is the production of an alcohol as a by-product. This creates the need for special purification steps, especially since most end uses of DOCA's require that they be neat or in an aprotic solvent, rather than a protic solvent such as an alcohol.
U.S. Pat. No. 4,067,883 teaches the formation of DOCA's from aromatic diols and a compound of the formula ##STR2## with the application of heat. This also produces alcohol by-products.
Accordingly, there is a need for a process to prepare DOCA's which is both energy effficient (i.e., has a high positive free energy), and has minimal by-product formation (especially the absence of protic by-products).